Re: [PSUBS-MAILIST] open source scrubber design

[MerlinSub@t-online.de]

400 Liter inside volume last 40 minute before a man catch heavy headache. (Sgt.Peppers)

Not running the scrubber and O2 bottle in a small sub will increase 
the co2 level to a still breathable but not very healty high ina short time. 
It will short your emergency reaction time in case of black ship to a short period.

On Eurosub and Peppers the first switch we take online after the the main battery switch is the scrubber. 
Dosent matter if the boat is still on the surface. 

vbr Carsten

<JimToddPsub@aol.com> schrieb:
> Rick,
>  
> I'd certainly agree with that; it's one reason George  Kittredge didn't 
> bother with O2 or scrubbers at all, just depended on what was  contained in the 
> volume of the sub.  Good reminder.  
>  
> I haven't yet calculated how long I could operate on test  dives on hull 
> air before activating the O2 or scrubbers.  Of course that  has to be 
> determined on shop dives.  What I was referring to is  the capacity after activating 
> the LS systems in a relatively small  sub.
>  
> Jim
>  
>  
> In a message dated 3/13/2011 5:12:19 P.M. Central Daylight Time,  
> landnsea1@hawaiiantel.net writes:
> 
> I would think it would as the larger the air  volume for a person to 
> breath, the longer it would take to drop the C02 level  to an unacceptable level 
> before needing to scrub??
>  
>  
> 
> 
> 
> From: _JimToddPsub@aol.com_ (mailto:JimToddPsub@aol.com)  
> Sent: Sunday, March 13, 2011 10:35 AM
> To: _personal_submersibles@psubs.org_ 
> (mailto:personal_submersibles@psubs.org)   
> Subject: Re: [PSUBS-MAILIST] open source scrubber  design
> 
> 
> 
> 
> Rick, would that matter?  It seems it would just be  based on the amount of 
> CO2 being generated via respiration.  It might  influence the way you set 
> up the circulation system.   Correct?
> JT
>  
>  
> In a message dated 3/13/2011 3:30:33 P.M. Central Daylight Time, 
> _landnsea1@hawaiiantel.net_ (mailto:landnsea1@hawaiiantel.net)   writes:
> 
> Cliff,
>  
> I noticed in your post below that you  mentioned "30 lbs of Sodasorb = 80 
> hours of life support for one man" What  internal volume are you basing that 
> on?
>  
> Rick
>  
> 
> 
> 
> From: _JimToddPsub@aol.com_ (mailto:JimToddPsub@aol.com)  
> Sent: Sunday, March 13, 2011 10:13 AM
> To: _personal_submersibles@psubs.org_ 
> (mailto:personal_submersibles@psubs.org)   
> Subject: Re: [PSUBS-MAILIST] open source scrubber  design
> 
> 
> 
> 
> Cliff,
>  
> 1. My first thought was to split the total amount of  Sodasorb into two 
> identical canisters, but then it occurred it might cut  operating costs to have 
> one smaller canister adequate for most  missions and a second larger 
> canister (sealed) plumbed in for longer  missions and long term life support.  
> That way you're not having to  dump as much unused Sodasorb. 
>  
> 2. In sizing canisters for one and two person subs, is  there some 
> relatively constant ratio between diameter and length, or should  the variability 
> just be in the length of the canisters (constant diameter)  when designing for 
> various capacities?
>  
> 3. What size canister(s) are you contemplating for your  next design?
>  
> I like the complete redundancy Alan referenced on the  DW2000, but 
> accessible space can get short in a hurry in very small subs.  Thanks for your 
> comments.
>  
> Jim
>  
>  
> In a message dated 3/13/2011 1:40:12 P.M. Central Daylight Time,  
> cliffordredus@sbcglobal.net writes:
> 
>  
> 
> Emile
>  
> When I build my boat, I to did some investigation into  commercially 
> available scrubber systems that would be applicable for  a one man psub.  I did 
> not find any that were economically  viable. While I agree with Leander that 
> fundamentally the scrubber is  not complicated, to make an efficient and 
> practical scrubber  takes some work.  I went through several iterations on  
> mine.  One of the key items is, as you mention, the fan.  ABS  requires 72 hours 
> of emergency life support after your primary mission  time and this has to 
> be able to run off the emergency battery  bank.  If you under size the fan 
> to minimize the power requirement to  the fan,  then the fan can not generate 
> sufficient differential  pressure across the fan to circulate the 
> contaminated air.  This is  particularly true if you use an axial flow fan rather 
> than a radial  centrifugal fan.  Axial fans are commonly installed on most PC  
> computers.  They are designed for high flow rate but low head.   I made the 
> mistake of using an axial flow fan on my first iteration of my  scrubber.  
> While it would last 80 hours ( the current load is  very small), the scrubber 
> effectiveness was not great probably because the  blades very stalling.  My 
> initial CO2 level would start at about  350 ppm but would build to 5000 ppm 
> (0.5 mole %) over 30  minutes.  My second iteration replaced the axial fan 
> with a small  radial centrifugal fan (squirrel cage) which developed four  
> times the head at about 1/4 of the flow rate.  The  current demand was only 
> slightly higher. This worked great while  still meeting the low current 
> requirment.
>  
> The scrubber absorbent choice to me is a no brainier.  Sodasorb  HP is what 
> is used most often these days for psubs  and re-breathers for divers. It is 
> easy to get and not very  expensive.   From a design perspective, after 
> sorting out the  fan, it comes down to how do want to handle the storage of the 
> emergency  Sodasorb.  There are three options, 1) cartridges for the 
> primary and  emergency absorbent, 2) scrubber sized to hold the primary and 
> emergency  absorbent 3) scrubber sized for the primary absorbent and spare  
> Sodasorb stored in bulk requiring refill when primary absorbent becomes  
> saturated. There are advantages and disadvantages to each  technique.  While 
> cartridges are easy to replace  in an  emergency situation, the spare cartridges 
> don't pack as  efficiently as bulk  absorbent.  For a small psub like mine,  
> this rules them out; I just did not have the room. I note that  the  
> Deepworker uses the option 2) .  For small one man psubs, I  think option 2 is 
> probably the best way to go.  The  disadvantage to this approach is that for non 
> emergency conditions, you  end of tossing a lot of partially used Sodasorb 
> after each  dive.  For a one person sub, this is not an issue but for more  
> than one, this makes this option not as attractive.  Also, because it  is 
> inexpensive, this is not a big deal for a one person sub.  This  option provides 
> the least stress in a stressful emergency as the operator  does not have to 
> worry about changing out the absorbent when it becomes  saturated.  On my 
> boat, I use option 3 primarily because of  the storage issue.  On my next one 
> person boat, I would go with  option 2.  Replacing 30 lbs of Sodasorb (80 
> hours of  life support for one man) is not a big deal given that it 
> simplifies  life.
>  
> While the manufactures of  these absorbents add a chemical that  turns the 
> absorbent a different color than white when it becomes  saturated, this is 
> not very practical to use as lighting in subs make  it hard to detect the 
> color change.  A better detection of a  saturated absorbent is a good CO2 
> sensor with an audible  alarm. 
>  
> So to me, it comes down to correctly specifying the fan and how  to package 
> the spare absorbent. 
>  
> Cliff
> 
> 
> 
> 
> 
> 
> 




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